Italian macroalgal herbaria in the 21st century: new roles in modern phycological research

In Europe, marine macroalgae have been collected and preserved since the late 17th century. This practice became popular in the two subsequent centuries, when several early naturalists with interest in algae produced some of the largest algal herbaria still available today (Carl Adolf Agardh and Jacob Georg Agardh, Pierre-Louis Crouan and Hippolyte-Marie Crouan, Friedrich Traugott Kützing, William Henry Harvey). As result, approximately one million and seven hundred thousand specimens are nowadays deposited in European herbaria (Mannino et al., 2020). In the past, herbarium specimens were mainly used for studies of algal taxonomy based on morphological features and species distributions. Nowadays they still play an important role in these research Sields, in fact even more important. For instance, herbarium specimens can clarify the taxonomic identity of genera and species (Wujek & Wynne, 2016). In the last decades, the possibility to extract and sequence DNA from herbarium specimens has resulted into taxonomic revisions, discovery of cryptic species and records of nonindigenous seaweeds. Sequences obtained from type specimens have played an especially important role, as they have allowed major advancements in algal phylogeny and classiSication. Nowadays, however, herbarium specimens of macroalgae serve more uses than they were originally intended. Algal collections have provided information for studies of algal biochemistry, physiology and phytopathology and have become a critical resource for studies of global change biology. Furthermore, the use of herbarium data in all these scientiSic research Sields has been greatly enhanced by the recent increasing specimen digitization and the development of online platforms. Italian herbaria host approximately 160,000 algal specimens. Although considerably lower in number than vascular plants, these collections represent a major scientiSic patrimony that has proved invaluable especially for studies of historical changes in coastal marine communities. As herbarium specimens may help in detecting shifts in species ranges, new introduction, species retreat or extinction, they are indeed true witnesses of biodiversity changes. In this framework, we present some recent research experiences based on the macroalgal herbaria's taxonomic revision and evaluation of vegetation changes. The taxonomic identity and geographical distribution of several macroalgae widespread along the Italian coasts has been clariSied using sequences obtained from type specimens, even for some species that play a key role as ecosystem engineers (e.g., the coralline red alga Lithophyllum stictiforme; Pezzolesi et al., 2019). For some geographical areas, such as the Lagoon of Venice, the Gulf of Trieste and the Conero Riviera, herbarium specimens allowed detailed reconstruction of historical changes in the macroalgal vegetation. For many Italian macroalgal herbaria (Armeli Minicante et al., 2025), digitization is ongoing or planned, within the framework of several initiatives. The metadata processing and sharing through the Global Biodiversity Information Facility (GBIF), according to international standards and the FAIR principles, will further increase the value of Italian herbaria as resources for science and outreach to the general public.